1. Field of the Invention
The invention relates to a manhole cover including a frame and a lid which is insertable in the frame and is provided with an insert plate on its upper surface.
The frame of such a manhole cover is inserted into the road surface and the lid is inserted into the frame and locked therein so that, when subjected to stress, it does not move or, worse yet, lift off from the frame. The frame and the lid of the manhole cover are customarily made of cast iron and it is known to provide profiled portions on the upper surface of the lid to improve the non-slip characteristics thereof, such profiled portions being produced simultaneously, if the lids are produced by casting, during the casting process. The profiled portions consist of irregularly disposed projections, such as, for example, protruding ribs or the like. These grid-like profiles which have closed, rectangular or square openings, are easily clogged with road dirt and are very difficult to clean. Furthermore, the grid-like profiles wear down after a period of time with the result that they are no longer safe for traffic, and then the entire lid must be replaced. In addition, the monotonous grid-like profiles spoil the appearance of the road, especially in pedestrian zones. Likewise, the same applies to manhole covers whose lids are filled with concrete or the like. In this case also, it is necessary to replace the entire lid once the concrete filling has become worn, and the concrete filling does not provide the lid with an attractive appearance.
2. Discussion of the Prior Art
A manhole cover including a frame and lid which have on their surfaces a corrugation formed of raised portions and grooves separating the raised portions from one another is disclosed in German Gebrauchsmuster (Utility Model) No. 1,956,898, wherein, if the lid is filled with concrete, the raised portions and grooves are provided in a corrugated plate which covers the concrete filling and is securely fixed thereto by anchoring means. When the raised portions of such a corrugated plate are worn down, it is necessary to replace the entire lid since the corrugated plate is securely anchored in the concrete filling. In addition, the appearance of the corrugated plate is not particularly aesthetically pleasing.